Re: [RFC v1 1/1] devtools: allow libraries with no global section

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Mar 06, 2024 at 05:14:15PM +0100, David Marchand wrote:
> On Wed, Mar 6, 2024 at 3:36 PM Paul Szczepanek <paul.szczepanek@arm.com> wrote:
> >
> > If a library has no global section in the version.map
> > allow it not to have symbols and not report it as an error.
> > This happens if a library doesn't export any functions
> > if they're all inline.
> >
> > Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>
> 
> Added Bruce.
> 
> Having a library without any actual code compiled is (I think) new in DPDK.
> 
> On the other hand, for headers only, there should be no need for a
> version.map file at all.
> 
> The current meson code expects that every library provides some files
> to compile via the sources variable and it expects a version.map file
> too.
> I wonder if we could skip the whole library generation at the
> lib/meson.build level.
> Something like:
> 
> diff --git a/lib/meson.build b/lib/meson.build
> index 179a272932..f0bbab6658 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -222,6 +222,10 @@ foreach l:libraries
>      includes += include_directories(l)
>      dpdk_includes += include_directories(l)
> 
> +    if sources.length() == 0
> +        continue
> +    endif
> +
>      if developer_mode and is_windows and use_function_versioning
>          message('@0@: Function versioning is not supported by
> Windows.'.format(name))
>      endif
> 
> No version.map, no check to update :-)
> 
Two thoughts/suggestions here:

* in original meson port we did have support for header only libraries - I
  think for rte_compat.h, but that was done away with when the header was
  just merged into EAL. See [1]
* for a header only lib - if we are prepared to forego being able to
  disable it - the easiest enablement path may be to not add the directory
  to the list of libraries, and just add the header file path to the global
  include path, or perhaps some other library include path. How to make it
  work best may depend on what the library does and what other DPDK libs, if
  any, it depends upon.

[1] http://git.dpdk.org/dpdk/tree/lib/meson.build?h=v18.11&id=0da7f445df445630c794897347ee360d6fe6348b#n72